This invention relates to the regeneration of carbonaceous adsorbent material, and more particularly, to a device for controlling the flow distribution of the adsorbent material through the regeneration vessel during the regeneration process.
In the field of atmospheric pollution control, it is known to use an adsorptive process for the desulfurization of flue gas. The principal underlying the process is the adsorption of sulfur dioxide (SO.sub.2) on carbonaceous adsorbent material and its conversion to sulfuric acid by combining with the oxygen and water vapor also present in the flue gas. The sulfuric acid is enriched adsorbatively in the porous system of the carbonaceous adsorbent, which is a material called "char" and is commonly in pellet form. The char pellets loaded with sulfuric acid are regenerated by a process in which the acid is decomposed to sulfur dioxide, carbon dioxide and water, with some consumption of the char. The sulfur dioxide-enriched gas is further processed as desired.
The regeneration of the saturated char can be accomplished by washing (wet regeneration) or by contacting it with hot sand (thermal regeneration). Wet regeneration produces dilute sulfuric acid (18% by weight) as a by-product, and because of the limited use for this by-product, thermal regeneration is the more practical method.
In thermal regeneration, an enclosed, refractory-lined vessel is utilized to contact the saturated char pellets with hot sand, which has been heated to approximately 815.degree. C. (1500.degree. F.). As the char pellets become heated, the reactions that occurred during the adsorption process are reversed, producing a concentrated stream of sulfur dioxide, water, carbon dioxide, and nitrogen. During regeneration, the hydrogen sulfate produced in the adsorption process is converted to water and sulfur trioxide which, in turn, is F.). to sulfur dioxide in the presence of the hot char and produces carbon dioxide by the combination of the liberated oxygen with the carbon in the char. In a like manner, the oxides of nitrogen are reduced to nitrogen, with the resultant production of additional carbon dioxide.
Sand is utilized as an inert, heat-transfer media in thermal regeneration and, as such, does not take part in the reactions occurring within the regenerator. Its sole function is to supply heat so that the reactions may take place. Regeneration is accomplished with the mixture of sand and char having a temperature in the range of 500.degree.-600.degree. C. (932.degree.-1202.degree. F.). The mixture of hot sand and char flows slowly down through the regeneration vessel, with the flow being controlled by a char-sand separator/feeder positioned below the discharge hopper of the vessel.
With thermal regeneration, a regeneration temperature with a high, heating velocity can be achieved. This results in a regeneration vessel of small volume and a short char residence time, or the time that the char is physically within the generator reactor as it flows therethrough. In addition, side reactions, e.g., with oxygen, which would consume additional char, can be eliminated.
To ensure proper and efficient regeneration it is necessary to ensure the uniform and continuous flow of the char-sand mixture through the vessel, with a minimum residence time therein. In the prior art, one means of controlling this flow through the vessel consisted of a single, cone structure, which was formed with a base having an outside diameter less than the inside diameter of the hopper portion of the vessel in which the flow control cone was mounted. In this manner, an annular passageway was created between the base of the cone and the inside diameter of the hopper. However, this prior art flow control cone had several disadvantages from a structural standpoint. For example, it was particularly difficult to mount the flow control cone in the reactor. The cone was generally secured to the hopper by a plurality of angle-iron support members, each of which was attached at one end to the circumference of the cone and at the other end to the inner surface of the hopper. These supporting members, of course, obstructed the flow path and, consequently, the flow passages were frequently plugged, causing clogging of the flow and making flow distribution difficult.